A novel function for the eukaryotic translation elongation factor 1A

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Abstract

The eukaryotic translation elongation factor 1A, eEF1A, a homolog of the bacterial EF1A (formerly known as EF-Tu), is a well-characterized ribosome associated factor, responsible for the delivery of aminoacyl-tRNAaa to the ribosomal A site. In contrast to this indirect interaction with the nascent polypeptide chain it is shown here for the first time that eEF1A also associates directly with the nascent polypetide chain distal to the peptidyl transferase center of the ribosome. This is demonstrated for a variety of nascent polypeptide chains of different length and sequence. Interestingly, unlike other ribosome associated factors, eEF1A also interacts with polypeptides after their release from the ribosome. It is further demonstrated that eEF1A does not bind to correctly folded full-length proteins, but interacts specifically with proteins that are unable to fold correctly in a cytosolic environment. This association was demonstrated both by photo-crosslinking and by a functional refolding assay. Furthermore, it is shown that the interaction of the nascent polypeptide chain with eEF1A can be competed out with a variety of short peptides. However, the found minimum length of 20-30 amino acids for these short peptides is significantly longer than typical binding sites in molecular chaperones or MHCs which is about seven to nine amino acids in length. The presence of charged aa-tRNAaa or uncharged tRNAaa in crosslinking experiments elicited a dose-dependent response similar to that seen in the competition experiments with short peptides. Gel-filtration demonstrated that eEF1A exhibits �quasi chaperone� activities, because eEF1A seems to be able to dissolve large complexes of oligomerized peptides and co-migrates with the dissolved peptide. Based upon the results of this work a model describing a novel function for eEF1A is presented.